Crystalline composition, device, and associated method

ABSTRACT

A composition including a polycrystalline metal nitride having a number of grains is provided. These grains have a columnar structure with one or more properties such as, an average grain size, a tilt angle, an impurity content, a porosity, a density, and an atomic fraction of the metal in the metal nitride.

BACKGROUND

The invention includes embodiments that may relate to a crystallinecomposition. The invention includes embodiments that may relate to anapparatus for making a crystalline composition, and to a deviceincluding the crystalline composition. The invention includesembodiments that may relate to a method of making and/or using thecrystalline composition.

Preparation of crystalline compositions, such as polycrystalline groupIII metal nitrides, may produce relatively fine powder particles orfilms of modest thickness. The powder form may have little or noappreciable mechanical or electrical bonding between the grains, and maynot be strongly bonded, dense or cohesive. For use as a sputter target,the bulk polycrystalline material should be strongly bonded, dense, andcohesive. Items made from the powder form may have an undesirable highresidual porosity and/or moisture sensitivity, which may allow for easeof disintegration and dissolution. For a crystalline growth source, anarticle should not easily disintegrate back into solution.

Several methods related to chemical vapor deposition may be capable offorming a polycrystalline metal nitride film. Some methods may sufferfrom a difficulty in scaling up and/or precision control of the gasphase reaction processes leading to poor quality control. Suchdifficulty may be due to a use of initially solid materials asreactants, or may be due to extreme reaction conditions. Sometimes, thefilms may contain undesirable levels of contaminants, which may makethose films relatively less suitable for use in, for example,ammonothermal crystalline growth.

Crystals having differing properties than those crystals currentlyavailable may be desirable. A method or process for making such crystalsand/or using the crystalline composition may be desirable. It may bedesirable to have an apparatus for making a crystalline composition, andto a device including the crystalline composition, that differs fromthose currently available.

BRIEF DESCRIPTION

In accordance with an embodiment of the invention, a compositionincluding a polycrystalline metal nitride having plurality of grains isprovided. The grains may have a columnar structure with one or moreproperties such as, an average grain size that is in a range of fromabout 10 nanometers to about 1 millimeter. The metal nitride may becharacterized by one or more of, an impurity content that is less thanabout 200 parts per million, a porosity in volume fraction that is in arange of from about 0.1 percent to about 30 percent, an apparent densitythat is in a range of from about 70 percent to about 99.8 percent, anatomic fraction of the metal that is in a range of from about 0.49 toabout 0.55.

In one embodiment, an article is provided that is formed from thecomposition. The composition may include the polycrystalline metalnitride.

In another embodiment, a device is provided that includes the article.The article is formed from the composition. The composition may includethe polycrystalline metal nitride.

DRAWINGS

FIG. 1 is a schematic side view of an apparatus according to oneembodiment of the invention;

FIG. 2 is a schematic side view of an apparatus in accordance with anembodiment of the invention;

FIG. 3 is a schematic side view of an apparatus according to oneembodiment of the invention;

FIG. 4 is a schematic side view of an apparatus in accordance with anembodiment of the invention;

FIG. 5 is a schematic side view of an apparatus according to oneembodiment of the invention;

FIG. 6 is a flow chart of a method for making a crystalline compositionaccording to one embodiment of the invention;

FIG. 7 is an SEM image showing a cross-section of polycrystallinegallium nitride;

FIG. 8 is an SEM image showing a growth surface of polycrystallinegallium nitride; and

FIG. 9 is a graph of the bend strength of gallium nitride.

DETAILED DESCRIPTION

The invention includes embodiments that may relate to a crystallinecomposition. The invention includes embodiments that may relate to anapparatus for making a crystalline composition, and to a deviceincluding the crystalline composition. The invention includesembodiments that may relate to a method of making and/or using thecrystalline composition.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it may be related. Accordingly, a value modified by aterm such as “about” may be not to be limited to the precise valuespecified. In at least one instance, the variance indicated by the termabout may be determined with reference to the precision of the measuringinstrumentation. Similarly, “free” may be combined with a term; and, mayinclude an insubstantial number, or a trace amount, while still beingconsidered free of the modified term unless explicitly stated otherwise.

According to one embodiment of the invention, a composition of apolycrystalline metal nitride is provided. The polycrystalline metalnitride may have a plurality of grains, and these grains may have acolumnar structure.

With reference to the grains, the grains may be characterized by one ormore properties. The properties may include a grain dimension. Otherproperties may include an average number of grains per unit volume, aninter-grain bend strength or a tilt angle of the grains relative to eachother.

The grain dimension may refer to either an average grain size or anaverage grain diameter. The grains may have a columnar structure; inthis case they have a major axis, and the average grain size refers toan average length of the grains along the major axis. Perpendicular tothe major axis may be one or more minor axes, and the average diameterof each grain may be determined with reference to the minor axes.Collectively, the average diameters of each of the grains may beaggregated and averaged to provide the average grain diameter. Anaverage, as used herein, may refer to the mean value.

The average grain size of the polycrystalline metal nitride may be in arange of greater than about 10 nanometers. In one embodiment, theaverage grain size may be in a range of from about 0.01 micrometer toabout 1 millimeter, while in certain other embodiments, the grain sizemay be in a range of from about 0.01 micrometer to about 30 micrometers,from about 30 micrometers to about 50 micrometers, from about 50micrometers to about 100 micrometers, from about 100 micrometers toabout 500 micrometers, from about 500 micrometers to about 1 millimeter,or greater than about 1 millimeter. The average grain diameter may belarger than about 10 micrometers. In one embodiment, the average graindiameter may be in a range of from about 10 micrometers to about 20micrometer, from about 20 micrometers to about 30 micrometers, fromabout 30 micrometers to about 50 micrometers, from about 50 micrometersto about 100 micrometers, from about 100 micrometers to about 500micrometers, from about 500 micrometers to about 1 millimeter, orgreater than about 1 millimeter.

An average number of grains per unit volume of the crystallinecomposition may indicate a grain average or granularity. The compositionmay have an average number of grains per unit volume of greater thanabout 100 per cubic centimeter. In one embodiment, the average number ofgrains per unit volume may be in a range of from about 100 per cubiccentimeter to about 1000 per cubic centimeter, from about 1000 per cubiccentimeter to about 10,000 per cubic centimeter, from about 10,000 percubic centimeter to about 10⁵ per cubic centimeter, or greater thanabout 10⁵ per cubic centimeter.

The grains may be oriented at a determined angle relative to each other.The orientation may be referred to as the tilt angle, which may begreater than about 1 degree. In one embodiment, the grain orientation ortilt angle may be in a range of from about 1 degree to about 3 degrees,from about 3 degrees to about 5 degrees, from about 5 degrees to about10 degrees, from about 10 degrees to about 15 degrees, from about 15degrees to about 30 degrees, or greater than about 30 degrees.

Properties that are inherent in or particular to one or more crystallinearticles produced according to an embodiment of the invention mayinclude bend strength, density, moisture resistance, and porosity, amongothers. The properties may be measured using the corresponding ASTMstandard test. Example ASTM numbers may include C1499.

The inter-grain bend strength of a thin film of one or more of thecrystals may be greater than about 20 MegaPascal (MPa). In oneembodiment, the inter-grain bend strength may be in a range of fromabout 20 MegaPascal to about 50 MegaPascal, from about 50 MegaPascal toabout 60 MegaPascal, from about 60 MegaPascal to about 70 MegaPascal,from about 70 MegaPascal to about 75 MegaPascal, from about 75MegaPascal to about 80 MegaPascal, from about 80 MegaPascal to about 90MegaPascal, or greater than about 90 MegaPascal. The bend strength mayindicate the grain to grain relationship at the inter-grain interfaceand/or the inter-grain strength.

The apparent density of crystalline articles may be greater than about 1gram per cubic centimeter (g/cc). In one embodiment, the density may bein a range of from about 1 gram per cubic centimeter to about 1.5 gramsper cubic centimeter, from about 1.5 grams per cubic centimeter to about2 grams per cubic centimeter, from about 2 grams per cubic centimeter toabout 2.5 grams per cubic centimeter, from about 2.5 grams per cubiccentimeter to about 3 grams per cubic centimeter, or greater than about3 grams per cubic centimeter. The crystalline composition density may bea function of, for example, the porosity or lack thereof, the crystalpacking arrangement, and the like.

The crystalline article may be aluminum nitride and may have an apparentdensity of less than about 3.26 gram per cubic centimeter at standardtest conditions. In one embodiment, the aluminum nitride crystallinearticle may have an apparent density in a range of from about 3.26 gramper cubic centimeter to about 2.93 gram per cubic centimeter, from about2.93 gram per cubic centimeter to about 2.88 gram per cubic centimeter,from about 2.88 gram per cubic centimeter to about 2.5 gram per cubiccentimeter, from about 2.5 gram per cubic centimeter to about 1.96 gramper cubic centimeter, or less than about 1.96 gram per cubic centimeter.

The crystalline article may be gallium nitride and may have an apparentdensity of less than about 6.1 gram per cubic centimeter at standardtest conditions. In one embodiment, the gallium nitride crystallinearticle may have an apparent density in a range of from about 6.1 gramper cubic centimeter to about 5.49 gram per cubic centimeter, from about5.49 gram per cubic centimeter to about 4.88 gram per cubic centimeter,from about 4.88 gram per cubic centimeter to about 4.27 gram per cubiccentimeter, from about 4.27 gram per cubic centimeter to about 4 gramper cubic centimeter, or less than about 4 gram per cubic centimeter.

The moisture resistance of the polycrystalline composition may begreater than about 0.001 gram/hour at 100 percent humidity at roomtemperature. The moisture resistance may be in a range of from about0.001 gram/hour to about 0.01 gram/hour, from about 0.01 gram/hour toabout 0.1 gram/hour, or less than about 0.1 gram/hour. The moistureresistance of the composition may indicate its resistance to intake ofmoisture, the hygroscopic proclivity of the composition, the surfacetreatment, the surface area per weight, the porosity, and/or the easewith which the composition may dissociate in a solution. The inter-grainbend strength may also contribute to the ease with which the compositionmay dissociate in a solution.

The porosity of the polycrystalline composition may be in a range ofless than about 30 percent by volume. In one embodiment, the porositymay be in a range of from about 30 percent to about 10 percent, fromabout 10 percent to about 5 percent, from about 5 percent to about 1percent, from about 1 percent to about 0.1 percent, or less than about0.1 percent by volume.

The metal of the metal nitride may include a group III metal. Suitablemetals may include one or more of aluminum, gallium, or indium. The “oneor more” refers to combination of metals in the metal nitride, and mayinclude compositions such as aluminum gallium nitride (AlGaN), and thelike.

A fraction of the metal, or metals, in the metal nitride may be selectedsuch that there is no excess metal in the metal nitride. In oneembodiment, the atomic fraction of the metal may be greater than about49 percent. In another embodiment, the atomic fraction may be in a rangeof from about 49 percent to about 50 percent, from about 50 percent toabout 51 percent, from about 51 percent to about 53 percent, from about53 percent to about 55 percent, or greater than about 55 percent.

The metal nitride composition may have an impurity. Impurities areunintended and/or undesirable inclusions in the final product, and mayresult from, for example, processing and handling. Other impurities mayresult from contaminants in raw materials. Some impurities may be moreclosely associated with select raw materials. Impurities aredistinguished from dopants in that the impurity does not intentionallyaid in the function of the product, or produces an undesirable effect inthe final product. Undesirable effects may include color, opticalabsorption, electrical properties (such as carrier mobility, resistance,or conductivity), or the like. Dopants are disclosed hereinbelow. Theimpurity may include residual oxygen resulting from the metal rawmaterial. In one embodiment, the oxygen content may be less than about100 parts per million (ppm). In another embodiment, the oxygen contentmay be in a range of from about 100 parts per million to about 70 partsper million, from about 70 parts per million to about 40 parts permillion, from about 40 parts per million to about 20 parts per million,or less than about 20 parts per million. Parts per million (PPM) refersto “by weight” unless otherwise indicated.

The impurity content may refer to any one of the impurities and not tothe total impurity amount. The impurity content may in thepolycrystalline composition may be less than about 200 parts permillion. In one embodiment, the impurity content may be in a range offrom about 200 parts per million to about 100 parts per million, fromabout 100 parts per million to about 50 parts per million, from about 50parts per million to about 40 parts per million, from about 40 parts permillion to about 30 parts per million, from about 30 parts per millionto about 20 parts per million, from about 10 parts per million to about5 parts per million, or less than about 5 parts per million.

With regard to dopants and dopant precursors (collectively “dopants”unless otherwise indicated), the electric, magnetic, and luminescentproperties of the metal nitride composition may be controlled by addingone or more of such dopants to the above composition during processing.Suitable dopants may include one or more of s or p block elements.Suitable s and p block elements may include, for example, one or more ofsilicon, germanium, magnesium, or tin. Other suitable dopants mayinclude one or more of transition group elements. Suitable transitiongroup elements may include one or more of, for example, zinc, scandium,zirconium, titanium, iron, vanadium, manganese, chromium, cobalt,copper, nickel, or hafnium. Suitable dopants may include one or more oflanthanides. Suitable lanthanides may include one or more of, forexample, praseodymium, europium, thulium, or erbium. Suitable dopantsmay produce an n-type material, or a p-type material.

Other suitable dopants may produce one or more of semi-insulatingmaterial, magnetic material, or luminescent material. In one embodiment,rather than constituting an impurity, oxygen may be intentionally addedas a dopant.

Suitable dopant concentration levels in the polycrystalline compositionmay be greater than about 10¹⁰ atoms per cubic centimeter. In oneembodiment, the dopant concentration may be in a range of from about10¹⁰ atoms per cubic centimeter to about 10¹⁵ atoms per cubiccentimeter, from about 10¹⁵ atoms per cubic centimeter to about 10¹⁶atoms per cubic centimeter, from about 10¹⁶ atoms per cubic centimeterto about 10¹⁷ atoms per cubic centimeter, from about 10¹⁷ atoms percubic centimeter to about 10¹⁸ atoms per cubic centimeter, from about10¹⁸ atoms per cubic centimeter to about 10²¹ atoms per cubiccentimeter, or greater than about 10²¹ atoms per cubic centimeter.

The composition may be formed as an article, particularly as anintermediate article. The intermediate article may be, for example, aboule or an ingot, and may be further processed. Post-formationprocessing of the boule or the ingot may yield, for example, a wafer.The wafer may further be worked upon and the processing may includebeing etched, polished, cut or diced. The wafer may be used for asputtering target, a transducer, or a device.

The shape of the processed article may be determined with reference toone or more requirements of the end usage. In one embodiment, thearticle has a shape with one or more dimensions of length, height, orwidth greater than about 0.5 millimeter. In another embodiment, thearticle has a shape with one or more dimensions of length, height, orwidth in a range of from about 0.5 millimeter to about 1 millimeter, orgreater than about 1 millimeter. In one embodiment, the article has athickness of greater than about 5 millimeters. In one embodiment, thearticle has a shape with two or more dimensions of length, height, orwidth greater than about 0.5 millimeter. In another embodiment, thearticle has a shape with two or more dimensions of length, height, orwidth in a range of from about 0.5 millimeter to about 1 millimeter,from about 1 millimeter to about 5 millimeters, from about 5 millimetersto about 10 millimeters, or greater than about 10 millimeters.

The surfaces of the article in one embodiment may be relatively smooth.The article may have one or more surfaces that have a root mean squareroughness of less than about 100 nanometers. In one embodiment, the rootmean square roughness may be in a range of from about 100 nanometers toabout 50 nanometers, from about 50 nanometers to about 10 nanometers,from about 10 nanometers to about 5 nanometers, from about 5 nanometersto about 3 nanometers, from about 3 nanometers to about 2 nanometers,from about 2 nanometers to about 1 nanometer, or less than about 1nanometer. The measurement techniques may include one or more of anatomic force microscope, mechanical and optical profiler, confocal laserscanning microscope, angle-resolved scattering, and total scattering.

The article may include one or more additional layers that differ fromeach adjacent layer. If a plurality of layers is present, suitableadditional layers may include one or more of a metal, an insulator, or asemiconductor. In a non-limiting example, a gallium nitride substratemay be provided, and an aluminum gallium nitride (AlGaN) layer may beepitaxially grown onto a surface of the substrate. Further, an n-dopedgallium nitride layer may be disposed over the AlGaN layer. Additionaland/or alternate layers may be added after processing steps, such asetching and/or polishing; and conductive contacts may be added to form,for example, a diode.

The articles may be incorporated into one or more transducer devices.Optionally, one or more structures may be secured to the article.Suitable structures are selected from a group consisting of a cathode,an anode, an electrically conducting lead, or a combination of two ormore thereof. Other suitable devices may include a piezoelectrictransducer, an optoelectronic device or an electronic device. Particularexamples of suitable devices may include one or more of a photovoltaicdiode, or a light emitting diode (LED), or a sensor, or a detector.

Referring now to the apparatus that includes an embodiment of theinvention, the apparatus may include sub systems, such as a housing, oneor more supply sources, and a control system.

The housing may include one or more walls, components, and the like. Thewalls of the housing may be made of a metal, a refractory material, orfused silica. In one embodiment, the housing may have an inner wall, andan outer wall spaced from the inner wall. An inner surface of the innerwall may define a chamber.

The walls of the housing may be configured (e.g., shaped or sized) withreference to processing conditions and the desired end use. Theconfiguration may depend on the size and number of components, and therelative positioning of those components, in the chamber. The chambermay have a pre-determined volume. In one embodiment, the housing may becylindrical with an outer diameter in a range of from about 5centimeters to about 1 meter, and a length of from about 20 centimetersto about 10 meters. The housing may be elongated horizontally, orvertically. The orientation of the elongation may affect one or moreprocessing parameters. For example and as discussed in further detailhereinbelow, for a horizontal arrangement, a series of crucibles may bearranged in a series such that a stream of reactants flow over thecrucibles one after another. In such an arrangement, the concentrationand composition of the reactant stream may differ at the first cruciblein the series relative to the last crucible in the series. Of course,such an issue may be addressed with such configuration changes asrearrangement of the crucibles, redirection of the reactant stream,multiple reactant stream inlets, and the like.

A liner may be disposed on the inner surface of the inner wall along theperiphery of the chamber. Suitable liner material may include graphiteor metal. The liner and other inner surfaces may not be a source ofundesirable contaminants. The liner may prevent or reduce materialdeposition on the inner surface of the inner wall. Failing theprevention of material deposition, the liner may be removable so as toallow the deposited material to be stripped from the inner wall during acleaning process or replacement of the liner.

Because the inner wall may be concentric to and spaced from the outerwall, the space may define a pathway between the inner wall and theouter wall for environmental control fluid to flow therethrough.Suitable environmental control fluids that may be used for circulationmay include inert gases. Environmental control fluid may include gas,liquid or supercritical fluid. An environmental control inlet may extendthrough the outer wall to the space. A valve may block the environmentalcontrol fluid from flowing through the inlet and into the pathway tocirculate between the inner and outer walls. In one embodiment, theinlet may be part of a circulation system, which may heat and/or coolthe environmental control fluid and may provide a motive force for thefluid. The circulation system may communicate with, and respond to, thecontrol system. Flanges, such as those meant for use in vacuum systems,may provide a leak proof connection for the inlet.

Suitable components of the housing may include, for example, one or moreinlets (such as raw material inlets and dopant inlets), outlets,filters, heating elements, cold walls, pressure responsive structures,crucibles, and sensors. Some of the components may couple to one or moreof the walls, and some may extend through the walls to communicate withthe chamber, even while the housing is otherwise sealed. The inlets andthe outlet may further include valves.

The inlets and the outlet may be made from materials suitable forsemiconductor manufacturing, such as electro polished stainless steelmaterials. The inlets and/or outlets may be welded to the respectivewall, or may be secured to the wall by one or more metal-to-metal seals.Optionally, the inlets and/or outlets may include purifiers. In oneembodiment, the purifier includes a getter material, for example azirconium alloy which may react with the contaminants to form therespective nitrides, oxides and carbides, thus reducing the probabilityof contamination in the final product. In one embodiment, the purifiersmay be placed in the inlets at the entrance to the chamber. Forreactions utilizing large quantities of ammonia the main concern forcontamination may be the presence of water due to hygroscopic nature ofammonia. The contamination of ammonia drawn from an ammonia tank mayincrease exponentially as the ammonia tank empties and when 70 percentof ammonia is reached, the tank may be replaced. Alternatively, apoint-of-use purifier may be utilized at the inlets. The use of apoint-of-use purifier may help in controlling the contamination inammonia thereby reducing ammonia wastage. Optionally, lower gradeammonia may be utilized along with the point-of-use purifier to obtainthe required grade of about 99.9999 percent.

The shape or structure of the inlets and outlet may be modified toaffect and control the flow of fluid therethrough. For example, an innersurface of the inlet/outlet may be rifled. The rifling may spin the gasflowing out through the ends and enhance mixing. In one embodiment, theinlets may be coupled together such that the reactants may pre-mixbefore they reach reaction zone or hot zone. Each of the inlets andoutlets may have an inner surface that defines an aperture through whichmaterial can flow into, or out of, the chamber. Valve apertures may beadjustable from fully open to fully closed thereby allowing control ofthe fluid flow through the inlets and the outlets.

The inlets may be configured to promote mixing of thenitrogen-containing gas and the halide-containing gas upstream of thecrucible(s), so as to promote uniform process conditions throughout thevolume of the chamber. One or more of the inlets may contain one or moreof baffles, apertures, frits, and the like, in order to promote mixing.The apertures, frits, and baffles may be placed within the chamberproximate to the hot zone or crucibles so as to control the flow of gasin the chamber, which may prevent or minimize the formation of solidammonium halide. The apertures, frits, and baffles may be placedupstream of the nearest crucible, with a distance of separation that isin a range from about 2 cm to about 100 cm, in order for mixing to becomplete prior to the onset of reaction with the contents of thecrucible. The presence of apertures and baffles may promote higher gasvelocities that promote mixing and inhibit back-flow of gases,preventing or minimizing the formation of solid ammonium halide.

One or more crucibles may be placed within the chamber. In oneembodiment, the number of crucibles within the chamber is about 6.Depending on the configuration of the chamber, the crucibles may bearranged horizontally and/or vertically within the chamber. The crucibleshape and size may be pre-determined based on the end usage of the metalnitride, the raw material types, and the processing conditions. For thepolycrystalline composition to be useful as a sputter target, the sizeof the crucible may be relatively larger than the required size of thesputter target. The excess of the polycrystalline composition may beremoved, for example, through etching or cutting to form the sputtertarget article. Such removal may eliminate surface contaminationresulting from contact with the crucible material.

The crucible may withstand temperatures in excess of the temperaturerequired for crystalline composition formation while maintainingstructural integrity, and chemical inertness. Such temperatures may be,greater than about 200 degree Celsius, in a range of from about 200degree Celsius to about 1200 degree Celsius, or greater than about 1200degrees Celsius. Accordingly, refractory materials may be suitable foruse in the crucible. In one embodiment, the crucible may include arefractory composition including an oxide, a nitride, or a boride. Thecrucible may be formed from one or more of silicon, aluminum, magnesium,boron, zirconium, beryllium, graphite, molybdenum, tungsten, or rheniumor their respective oxides, nitrides or borides. In one embodiment, aremovable graphite liner may be placed inside the crucible so as tofacilitate easy removal of the polycrystalline composition.

Suitable sensors may include one or more of pressure sensors,temperature sensors, and gas composition sensors. The sensors may beplaced within the chamber, and may communicate the process parameters inthe chamber to the control system.

Suitable supply sources may include one or more of an energy source, anitrogen-containing gas source, a carrier gas source, ahalide-containing gas source, a raw material source (sometimes referredto as a reservoir), environmental control fluid source, and the like.

The energy source may be located proximate to the housing and may supplyenergy, such as thermal energy, plasma energy, or ionizing energy to thechamber through the walls. The energy source may be present in additionto, or in place of, the heating elements disclosed above. In oneembodiment, the energy source may extend along an outward facing surfaceof the outer wall of the housing. The energy source may provide energyto the chamber.

The energy source may be a microwave energy source, a thermal energysource, a plasma source, or a laser source. In one embodiment, thethermal energy may be provided by a heater. Suitable heaters may includeone or more molybdenum heaters, split furnace heaters, three zone splitfurnaces, or induction heaters.

Sensors may be placed within the chamber. The sensors may be capable ofwithstanding high temperature and elevated or reduced pressure in thechamber and be chemically inert. The sensors may be placed proximate tothe crucible, and/or may be placed at the inlets. The sensors maymonitor process conditions such as the temperature, pressure, gascomposition and concentration within the chamber.

The nitrogen-containing gas source may communicate through a first inletwith the chamber. The nitrogen-containing gas source may include one ormore filters, purifiers, or driers to purify and/or dry thenitrogen-containing gas. In one embodiment, the nitrogen-containing gasmay be produced at the source. The purifier may be able to maintainpurity levels of the nitrogen-containing gas up to or abovesemiconductor grade standards for purity. Suitable nitrogen-containinggases may include ammonia, diatomic nitrogen, and the like. Where thepresence of carbon is not problematic, nitrogen-containing organics maybe used.

Controlling the aperture of the associated valve allows control of theflow rate of the nitrogen-containing gas into the chamber. Unlessotherwise specified, flow rate will refer to volumetric flow rate.Processing considerations, sample size, and the like may determine anappropriate flow rate of the gas. The flow rate of nitrogen-containinggas may be greater than about 10 (standard) cubic centimeters perminute. In one embodiment, the flow rate of nitrogen-containing gas maybe in a range of from about 10 cubic centimeters per minute to about 100cubic centimeters per minute, from about 100 cubic centimeters perminute to about 200 cubic centimeters per minute, from about 200 cubiccentimeters per minute to about 500 cubic centimeters per minute, fromabout 500 cubic centimeters per minute to about 1200 cubic centimetersper minute, from about 1200 cubic centimeters per minute to about 2000cubic centimeters per minute, from about 2000 cubic centimeters perminute to about 3000 cubic centimeters per minute, from about 3000 cubiccentimeters per minute to about 4000 cubic centimeters per minute, fromabout 4000 cubic centimeters per minute to about 5000 cubic centimetersper minute, or greater than about 5000 cubic centimeters per minute.

The carrier gas source may communicate with the chamber through aninlet, or may share the first inlet with the nitrogen-containing gas.Pre-mixing the nitrogen-containing gas with the carrier gas may dilutethe nitrogen-containing gas to a determined level. Because thenitrogen-containing gas may be diluted with the carrier gas, which maybe inert, the likelihood of formation of certain halide solids proximateto the first inlet in the chamber may be reduced. Suitable carrier gasesmay include one or more of argon, helium, or other inert gases. In oneembodiment, the carrier gas inlet is positioned so that a stream ofcarrier gas may impinge on a stream of nitrogen-containing gas exitingthe first inlet. Dopants may be entrained in the carrier gas, in oneembodiment, for inclusion in the polycrystalline composition.

The halide-containing gas source may communicate through a second inletwith the chamber. As with the nitrogen-containing gas source, thehalide-containing gas source may include one or more filters, purifiers,driers, and the like, so that the halide-containing gas be purifiedand/or dried at the source. The halide-containing gas may be produced atthe source. Suitable halide-containing gases may include hydrogenchloride and the like.

Controlling the aperture of the associated valve allows control of theflow rate of the halide-containing gas into the chamber. Processingconsiderations, sample size, and the like, may determine an appropriateflow rate of the gas. The flow rate of halide-containing gas may begreater than about 10 (standard) cubic centimeters per minute. In oneembodiment, the flow rate of halide-containing gas may be in a range offrom about 10 cubic centimeters per minute to about 50 cubic centimetersper minute, from about 50 cubic centimeters per minute to about 100cubic centimeters per minute, from about 100 cubic centimeters perminute to about 250 cubic centimeters per minute, from about 250 cubiccentimeters per minute to about 500 cubic centimeters per minute, fromabout 500 cubic centimeters per minute to about 600 cubic centimetersper minute, from about 600 cubic centimeters per minute to about 750cubic centimeters per minute, from about 750 cubic centimeters perminute to about 1000 cubic centimeters per minute, from about 1000 cubiccentimeters per minute to about 1200 cubic centimeters per minute, orgreater than about 1200 cubic centimeters per minute.

The halide-containing gas may flow into the chamber from thehalide-containing gas source through the second inlet. As with thenitrogen-containing gas, the halide-containing gas may be pre-mixed withthe carrier gas to dilute the halide-containing gas to a determinedlevel. The dilution of the halide-containing gas with an inert, carriergas may reduce the likelihood of formation of certain halide solids inthe second inlet, proximate to the chamber. Such a formation mightreduce or block the flow therethrough. Optionally, the carrier gas inletmay be positioned such that a stream of carrier gas may impinge on astream of halide-containing gas exiting the second inlet or entering thechamber. In one embodiment, dopants may be entrained in the carrier gasfor inclusion in the polycrystalline composition.

The halide-containing gas and the nitrogen-containing gas may beintroduced into the chamber in an order that determine properties of thepolycrystalline composition. The manner may include simultaneousintroduction at a full flow rate of each component fluid (gas, liquid,or supercritical fluid). Other suitable introduction manners may includepulsing one or more of the components, varying the concentration and/orflow rate of one or more components, or staggered introductions, forexample, to purge the chamber with carrier gas.

The halide-containing gas and the nitrogen-containing gas inlets may bedisposed such that the exit end is located in the hot zone in thechamber. In one embodiment, one or more inlet is located in a region ofthe chamber that, during use, has a temperature of greater than about341 degree Celsius at 1 atmosphere, or a temperature in a range of fromabout 341 degree Celsius to about 370 degree Celsius, or greater thanabout 370 degrees Celsius.

The ratio of flow rate of the nitrogen-containing gas to the flow rateof the halide-containing gas may be adjusted to optimize the reaction.In one embodiment, the ratio of flow rate of the nitrogen-containing gasto the flow rate of halide-containing gas may be in a range of fromabout 30:1 to about 15:1, from about 15:1 to about 1:1, from about 1:1to about 1:10, or from about 1:10 to about 1:15.

The raw material source may communicate through the raw material inletand into the crucible, which is in the chamber. As with the othersources, the raw material source may include one or more filters,driers, and/or purifiers. Particularly with reference to the rawmaterial source, purity of the supplied material may have adisproportionately large impact or effect on the properties of the finalpolycrystalline composition. The raw material may be produced just priorto use and may be kept in an inert environment to minimize or eliminatecontamination associated with atmospheric contact. If, for example,hygroscopic materials are used, or materials that readily form oxides,then the raw material may be processed and/or stored such that the rawmaterial does not contact moisture or oxygen. Further, because the rawmaterial can be melted and flowed into the chamber during processing, inone embodiment, differing materials may be used in a continuous processthan might be available for use relative to a batch process. At leastsome of such differences are disclosed herein below.

Suitable raw materials may include one or more of gallium, indium, oraluminum. Other suitable raw materials may include one or more ofsilicon, germanium, or boron. Yet other suitable raw materials may beselected from alkaline earth elements, transition metal elements, thelanthanides, or the actinides. In one embodiment, the raw material mayhave a purity of 99.9999 percent or greater. In another embodiment, thepurity may be greater than about 99.99999 percent. The raw material maybe a gas; a liquid solution, suspension or slurry; or a molten liquid.The residual oxygen in the metal may further be reduced by heating undera reducing atmosphere, such as one containing hydrogen, or under vacuum.

While all of the materials needed for production may be sealed in thechamber during operation in one embodiment; in another embodiment,various materials may be added during the process. For example, the rawmaterial may flow through the raw material inlet, out of an exit end,and into a crucible within the chamber. Where there is a plurality ofcrucibles, multiple raw material inlets, or one inlet having multipleexit ends, may be used to flow raw material into individual crucibles.In one embodiment, the raw material inlet may be mounted on a linearmotion feed-through structure. Such feed-through structures may allowthe translation of the exit end of the raw material inlet from crucibleto crucible.

The flow and the flow rate of raw material to, and through, the rawmaterial inlet may be controlled by a valve. The valve may be responsiveto control signals from the control system. While the flow rate of theraw material may be determined based on application specific parameters,suitable flow rates may be larger than about 0.1 kilogram per hour. Inone embodiment, the flow rate may be in a range of from about 0.1kilogram per hour to about 1 kilogram per hour, from about 1 kilogramper hour to about 5 kilograms per hour, or greater than about 5kilograms per hour.

The dopant inlet may be in communication with a reservoir containingdopants and the chamber. The reservoir may be made of material compliantto semiconductor grade standards. The reservoir may have provision topurify/dry the dopants. In one embodiment, the reservoir may haveliners. The liners may prevent corrosion of the reservoir material, orreduce the likelihood of contamination of the dopants by the reservoir.

The dopant source may be separate, or may be co-located with one or moreof the other materials being added during processing. If addedseparately, the dopants may flow directly into a crucible by exiting anend of the dopant inlet. As mentioned, the dopant may be introduced bypre-mixing with, for example, the raw material, the carrier gas, thehalide-containing gas, or the nitrogen-containing gas. Metering of thedopant may control the dopant concentration levels in thepolycrystalline composition. Similarly, the placement of the dopant inthe polycrystalline composition may be obtained by, for example,pulsing, cycling, or timing the addition of the dopant.

Suitable dopants may include dopant precursors. For example, silicon maybe introduced as SiCl₄. Where carbon is a desired dopant, carbon may beintroduced as a hydrocarbon, such as methane, methylene chloride, orcarbon tetrachloride. Suitable dopants may include a halide or ahydride. In situations where carbon is a desired dopant, or aninconsequential contaminant, metals may be introduced as anorganometallic compound. For example, magnesium may be introduced asMg(C₅H₅)₂, zinc as Zn(CH₃)₂, and iron as Fe(C₅H₅)₂. The flow rate ofdopant precursors may be greater than about 10 (standard) cubiccentimeters per minute. In one embodiment, the flow rate of the dopantprecursors may be in a range of from about 10 cubic centimeters perminute to about 100 cubic centimeters per minute, from about 100 cubiccentimeters per minute to about 500 cubic centimeters per minute, fromabout 500 cubic centimeters per minute to about 750 cubic centimetersper minute, from about 750 cubic centimeters per minute to about 1200cubic centimeters per minute, or greater than about 1200 cubiccentimeters per minute. Alternatively, the dopant may be added inelemental form, for example, as an alloy with the raw material. Othersuitable dopants may include one or more of Si, O, Ge, Mg, Zn, Sc, Ti,V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Sn, Hf, Pr, Eu, Er, or Tm.

The outlet, and corresponding valve, may control the release of materialthat is inside of chamber. The released material may be vented toatmosphere, or may be captured, for example, to recycle the material.The released material may be monitored for composition and/ortemperature by an appropriate sensor mounted to the outlet. The sensormay signal information to the control system. Because contamination maybe reduced by controlling the flow of material through the chamber inone direction, the polycrystalline composition may be removed from thechamber by an exit structure in the wall at the outlet side.

The outlet may be coupled to an evacuation system. The evacuation systemmay be capable of forming a pressure differential in the chamberrelative to the atmospheric pressure. Suitable pressure differential maybe as low as about 10⁻⁷ millibar. In one embodiment, the pressuredifferential may be in a range of from about 10⁻⁷ millibar to about 10⁻⁵millibar, or less than about 10⁻⁵ millibar. In one embodiment, thepressure differential may be in a range of from about 50 Torr to about 1Torr, from about 1 Torr to about 10⁻³ Torr, from about 10⁻³ Torr toabout 10⁻⁵ Torr, or less than about 10⁻⁵ Torr. The evacuation may beused for pre-cleaning, or may be used during processing.

The outlet may be heated to a temperature, which may be maintained, thatis greater than the temperature where the vapor pressure of an ammoniumhalide that might be formed during processing is greater than theprocess pressure, for example, one bar. By maintaining a temperatureabove the sublimation point of ammonium halide at the reactor pressure,the ammonium halide might flow into a trap or may be precluded fromforming or solidifying near the outlet once formed.

The control system may include a controller, a processor incommunication with the controller, and a wired or wireless communicationsystem that allows the controller to communicate with sensors, valves,sources, monitoring and evaluating equipments, and the like.

The sensors within the chamber may sense conditions within the chamber,such as the temperature, pressure, and/or gas concentration andcomposition, and may signal information to the controller. Flow ratemonitors may signal information about the flow rate through thecorresponding inlet or outlet to the controller. The controller (via theprocessor) may respond to the information received, and may controldevices in response to the information and pre-determined instructionparameters. For example, the controller may signal the energy source toprovide thermal energy to the chamber. The controller may signal one ormore valves to open, close, or open to a determined flow level duringthe course of polycrystalline composition synthesis. The controller maybe programmed to implement a method of growing polycrystallinecompositions according to embodiments of the invention.

The resultant polycrystalline composition may be a metal nitride. Themetal nitride may be doped to obtain one or more of an n-doped or ap-doped composition. The metal nitride may be a metallic,semiconducting, semi-insulating or insulating material. Further, each ofthese compositions may be a magnetic or a luminescent material.

The working of the apparatus and the function of the various componentsare described below with reference to illustrated embodiments. Referringto the drawings, the illustrations describe embodiments of the inventionand do not limit the invention thereto.

An apparatus 100 in accordance with an embodiment is shown in FIG. 1.The apparatus 100 may be used for preparing a metal nitride material,and may include a housing 102 having a wall 104. The wall 104 may havean inner surface 106 that defines a chamber 108. An energy source 110may be located proximate to the wall 104. A first inlet 112 and a secondinlet 114 extend through the wall 104. The inlets 112, 114 define anaperture through which material can flow into, or out of, the chamber108. An outlet 118 extends through the wall 104 to the chamber 108. Acrucible 120 may be disposed in the chamber 108. A liner (not shown) mayline the inner surface 106 of the wall 104.

The energy source 110 may be a thermal energy source, such as a ceramicheater. The inlets 112, 114 and the outlet 118 may be electro polishedstainless steel suitable for semiconductor grade manufacturing. Thecrucible 120 may include boron nitride, and the inert liner may includegraphite.

During operation, a raw material may be filled into the crucible 120,and the crucible may be pre-loaded into the chamber. One or more dopantsmay be placed in the crucible with the raw material. After loading, thecrucible 120 may be sealed by a sealing mechanism (not shown).

A nitrogen-containing gas may flow through the first inlet 112 into thechamber 108. The nitrogen-containing gas may include ammonia, and mayinclude a carrier gas for pre-dilution. A halide-containing gas may flowthrough the second inlet 114 and into the chamber 108. Thehalide-containing gas may include hydrogen chloride. Thehalide-containing gas may be pre-diluted with a carrier gas. Unreactedgases and/or other waste materials may be removed from the chamber 108through the outlet 118. The chamber 108 may be purged by flowing ingases through the inlets 112, 114 and out through the outlet 118 priorto, crystalline composition formation. The outflow, optionally, may bemonitored to detect the impurity level of the out-flowing gas, which mayindicate when a sufficient purge has been achieved.

The energy source 110 may be activated. Activating the energy source 110may increase the temperature within the chamber 108 to pre-determinedlevel and at a pre-determined rate of temperature increase. An area,within the chamber 108 and proximate to the crucible 120, may define ahot zone or reaction zone (not shown).

The raw material, already in the crucible 120, may respond to contactwith the nitrogen-containing gas in the presence of thehalide-containing gas, and at the determined temperature, by reacting toform a nitride of the metal, that is, the polycrystalline composition.

After the polycrystalline composition has been formed, the housing 102may be opened at the outlet side. Opening on the outlet side maylocalize any introduced contaminants to the chamber 108 caused by theopening to the chamber side proximate to the outlet 118. Localizing thecontaminants proximate to the outlet 118 may reduce the distance thecontaminants must travel to purge from the chamber 108, and may confinethe path of the contaminants to regions in which the contaminants areless likely to contact any grown crystal, or crystalline compositiongrowing surface (such as an inner surface of the crucible 120). Inaddition, not opening the housing on the inlet side may decrease thelikelihood of a leak proximate to the inlet during a subsequent run.Thus, such a configuration may reduce the chance of contaminantscontaminating the produced crystals.

An apparatus 200 in accordance with an embodiment is shown in FIG. 2.The apparatus 200 may include a housing 202, and an energy source 204proximate to the housing 202. The housing 202 may include an inner wall206 and an outer wall 208. An inlet 209 may extend through the outerwall 208, but may stop short of the inner wall 206. The outer wall 208may have an outward facing surface. An inward facing surface or innersurface 212 of the inner wall 206 may define a chamber 214.

The inner wall 206 may be nested within, and spaced from, the outer wall208. The space between the walls 206 and 208 may be used to circulate anenvironmental control fluid that may enter the space through the inlet209 configured for that purpose. The outer wall 208 may be formed frommetal, while the inner wall 206 may be made of quartz. The energy source204 may be proximate to the outer wall 208.

A first inlet 216, a second inlet 218, a raw material inlet 224, adopant inlet 232, and an outlet 226 may extend through the inner andouter walls 206 and 208. A plurality of valves 215, 220, 223, 233 may bedisposed, one per tube, within the feed tubes that extend from sourcesto the corresponding inlets 216, 218, 224, 232. The individual feedtubes are not identified with reference numbers. And, the outlet 226 mayhave a valve 227 that may allow or block the flow of fluid therethrough.

The first inlet 216 may communicate with a nitrogen-containing gassource 217 and flow a nitrogen-containing gas into the chamber 214. Thenitrogen-containing gas may include ammonia. The nitrogen-containing gasmay be diluted with the carrier gas. The carrier gas may be argon, andmay be controllable separately from the nitrogen-containing gas flow.The second inlet 218 may be in communication with a halide-containinggas source 219. The second inlet 218 may allow a halide-containing gasto flow from the halide-containing gas source 219 into the chamber 214.The valve 220 may control the flow of the halide-containing gas from thehalide-containing gas source 219 through the second inlet 218 and intothe chamber 214. The halide-containing gas may include hydrogenchloride, which may have been diluted with the carrier gas. The rawmaterial inlet 224 may communicate with a raw material reservoir 222. Anexit end of the raw material inlet 224 may be positioned so as to flowraw material leaving the inlet 224 into a crucible 230. The valve 223may control the flow of the raw material from the reservoir 222 throughthe raw material inlet 224 and into the chamber 214. The raw materialmay include molten gallium.

The dopant source (not shown) may communicate with the chamber 214through the dopant inlet 232. The valve 233 may be switched on/off toopen or block a flow of dopant from the dopant source into the chamber214. In the illustrated embodiment, the dopant includes silicon, whichmay be in the form of SiCl₄.

The outlet 226 may allow for excess material to exit the chamber 214.The valve 227 may open or close, and by closing, a back pressure mightbe built up as additional materials are flowed into the chamber 214 andthe temperature is increased.

A plurality of crucibles 230 may be provided in the chamber 214. Thecrucibles 230 may be arranged horizontally relative to each other.Sensors 236 and 237 may be provided to monitor the pressure andtemperature, or other process parameters within the chamber 214.

As disclosed hereinabove, the environmental control fluid may flow inthe space between the walls through the inlet 209. The inlet 209 maycommunicate with a circulation system (not shown) to circulate the fluidin the space between the walls. The inlet 209 may include a valve 211 toadjust or optimize the circulation in the space between the walls.Flanges 210 meant for vacuum systems may be used to form a leak proofconnection. The fluid circulation system may have provision to heat orcool the fluid. The chamber 214, along with its contents, may be cooledor heated through this arrangement.

A control system may include a controller 234 that may communicate withthe various components as indicated by the communication lines. Throughthe lines, the controller 234 may receive information, such as signals,from sensors 236, 237. The controller 234 may signal to one or more ofthe valves 215, 220, 223, 227, 233, which may respond by opening orclosing. The valve 211 may communicate with the controller 234, andthrough which the controller 234 may control the flow of theenvironmental control fluid from the circulation system. Thus, thecontroller 234 may monitor and may control the overall reactionconditions.

Prior to operation, the chamber 214 may be evacuated. The controller 234may activate the valve 227 and a vacuum pump (not shown) to evacuate thechamber 214. The chamber 214 may be flushed with inert carrier gas. Theenergy source 204 may be activated to heat, and thereby volatilize, anyvolatile contaminants. The successive evacuation and purging may removethe contaminants from the chamber 214.

During operation, the controller may activate the valve 223 to start aflow of raw material from the reservoir 222 to the crucibles 230 throughthe raw material inlet 224. The dopant may be flowed into the cruciblethrough the dopant inlet 232 in response to the opening of thecorresponding valve 233. The controller may adjust the rates of flow ofmaterials by adjusting the degree to which the corresponding valves areopen or closed. The controller 234 may communicate with the sensors 236,237. The temperature and pressure within the chamber may be raised todetermined levels by the controller 234 activating the energy source204, and/or adjusting the outlet valve 227.

Once the desired temperature and pressure has been attained, thenitrogen-containing gas may be introduced in the chamber 214 through thefirst inlet 216. Alternatively, the nitrogen-containing gas may beintroduced in the chamber in the beginning of the heating cycle. Thehalide-containing gas may be flowed in through the second inlet 218. Thecontroller may adjust the flow rate of these gases by controlling therespective valves 215, 220.

The raw material including the dopants may react with thenitrogen-containing gas in the presence of the halide-containing gas.The reaction may proceed until the raw material reacts to form the metalnitride. In the illustrated embodiment, a silicon doped gallium nitridemay be formed.

FIG. 3 is a schematic representation of an apparatus 300 in accordancewith an embodiment. The apparatus 300 may include a housing 302, thehousing 302 having a wall 304, the wall 304 having an inner surface 306and an outer surface 308. The inner surface 306 of the wall 304 maydefine a chamber 310, within which reaction takes place to form thenitride. The apparatus 300 further may include an energy source 314, araw material source 328, a dopant source 338, a carrier gas source (notshown), a nitrogen-containing gas source 318, and a halide-containinggas source 324. Tubing may connect the various sources 328, 338, 318,324 to the chamber 310 via corresponding inlets 330, 340, 316, 322. Eachinlet 330, 340, 316, 322 may have a corresponding valve 329, 341, 317,323 disposed between the corresponding source 328, 338, 318, 324 and thehousing 302. Coupled to the inner surface 306 may be a pressure sensor352 and a temperature sensor 354. An outlet 344, with a correspondingvalve 345, extends through the wall 304. A control system includes acontroller 350 that communicates with each valve 317, 323, 329, 341, 345and each sensor 352, 354.

Crucibles 334 may be disposed within the chamber 310, and may be stackedone over the other to obtain a vertical configuration. The cruciblematerial may be fused silica. A liner 335 is disposed along the crucible334. The liner may be of graphite.

A graphite liner 312 may line the inner surface 306 of the inner wall304. The liner 312 may reduce or prevent material deposition on theinner wall 304. A removable liner 312 may facilitate cleaning betweenuses. An outlet heater 358 adjoins the outlet 344. A set of baffles 362may be provided within the chamber. The baffles shown in the figure is adiagrammatic representation including fins and/or blades, which promotemixing in a determined manner.

Prior to use, the chamber 310 may be evacuated through the outlet 344.The evacuated chamber 310 may be purged with inert carrier gas. Onceevacuated and purged, the chamber 310 may be sealed and the controller350 may activate the energy source 314, which adjoins the wall 304 alongthe outer surface 308, to supply thermal energy to the chamber 310.Pre-heating in this manner may remove volatile contaminants. Thecontroller 350 may signal the valve 329 and allow raw material to flowfrom the raw material source 328 into the chamber 310 through the rawmaterial inlet 330. The raw material inlet 330 may be maintained at atemperature above the melting point of the metal to facilitate the flowof the raw material. The raw material may include a mixture of gallium,indium, and aluminum. The dopant may include magnesium, and may be addedto, or metered into, the flow of raw material. The raw material inlet330 may be configured such that the raw material flows into eachcrucible from open ends of the raw material inlet 330.

Because materials are now flowing into a sealed chamber 310, the outlet344 may allow out flow of material, such as unreacted gas. The flow rateof gases from the chamber 310 may be controlled by the controller 350signaling the valve 345. The outlet heater 358 may maintain the outlet344 at a pre-determined temperature. Heating the outlet 344 may decreaseor prevent the formation in the outlet of solids such as ammoniumhalides, which may interfere with fluid flow through the outlet 344.

With the raw material and dopant disposed within a crucible, and thechamber maintained at the pre-determined temperature, the controller 350may control the appropriate valves to allow for a flow ofnitrogen-containing gas and of halide-containing gas to begin flowinginto the chamber 310. The gases may contact the raw material and reactto form the polycrystalline composition, doped with any dopant thatmight be present.

FIG. 4 is a schematic view of an apparatus 400 detailing the inlets inaccordance with an embodiment. The apparatus 400 may include a housing402 having a wall 404, the wall 404 may have an inner surface 406 and anoutward facing surface 408, as illustrated in the figure. The wall 404may be radially spaced from an axis 409. An energy source 410 may beprovided proximate to the outer surface 408. The inner surface 406 ofthe wall 404 may define a chamber 412.

The apparatus 400 may further include inlets 416 and 418. The inlet 416,in one embodiment, may be a single walled tube, and extends into thechamber 412 through the wall 404. The inlet 416 may be nested within,and spaced from the inner surface 406 of the wall 404. An exit end ofthe inlet 416 may define an aperture 422. A baffle 424 may adjoin theaperture 422. The spacing between the inlet 416 and the inner surface406 of the wall 404 may define the inlet 418. Further, an aperture oropening 426 may be provided in the inlet 418. A crucible 430 may bedisposed within the chamber 412.

A halide-containing gas may be introduced into the chamber 412 from asource (not shown) through the inlet 416, and a nitrogen-containing gasmay be introduced into the chamber 412 from a source (not shown) throughthe inlet 418. The inlets 416 and 418 may be configured such that thebaffle 424 provided in the inlet 416 may assist in proper mixing of thegases flowing in to the chamber 412 through the inlets.

The apparatus 400 may further include components not shown in the figuresuch as, a control system including a controller which may control theoverall reaction, valves for adjusting and/or controlling the flow ofmaterials to and/or from the chamber, inlets for introducing rawmaterials and/or dopants into the chamber, sources from where rawmaterials and/or dopants may be flowed into the chamber, sensors formonitoring the temperature, pressure and composition within the chamber,and the like. The working of the apparatus may be explained withreference to above described embodiments.

FIG. 5 is a schematic side view of an apparatus 450 detailing theinlets, in accordance with yet another embodiment. The apparatus 450 mayinclude a housing 452, having a wall 454 with an inner surface 456 andan outer surface 458. The wall 454 may be radially spaced from an axis457. An energy source 460 may be provided proximate to the outer surface458. The inner surface 456 of the wall 454 may define a chamber 464.

The apparatus may further include an inlet 468. The inlet 468 may benested within, and spaced from the inner surface 456 of the wall 454.The inlet 468 may extend into the chamber 464 and the exit end of theinlet 468 may include a frit 470. An inlet 474 may be formed in thespace between the inlet 468 and the inner surface 456 of the wall 454.At a pre-determined distance from the inlets 468, 474, a baffle 480 maybe provided within the chamber 464. The baffle 480 may further includean aperture 482.

The inlet 468 may be in communication with a halide-containing gassource (not shown) and may flow in the halide-containing gas to thechamber 464 through the frit 470. The frit may filter thehalide-containing gas thus reducing contamination. The frit may alsodiffuse the gas over a wider surface area. A nitrogen-containing gas maybe introduced into the chamber 464 through the inlet 474. The baffle 480with an aperture 482 may promote pre-mixing of the gases. The apparatus450 may include at least one crucible containing raw materials. Theapparatus 450 may further include components not shown in the figuresuch as, a control system, sensors which may communicate with thechamber and the control system, valves to control the flow of gases andthe raw materials into the chamber, and the like. The working of theapparatus may be explained with reference to above describedembodiments.

FIG. 6 is a flow chart depicting a method 500 for preparing a metalnitride in accordance with an embodiment of the invention. The methodstarts by evacuating, purging, and otherwise decontaminating a chamberto remove trace impurities, and then sealing the chamber to avoidrecontamination (step 502). The environment in the chamber is adjustedto determined levels. The temperature of the chamber may be maintainedbetween about 800 degree Celsius to about 1300 degree Celsius, and thepressure within the chamber may be greater than about ambient.

Raw material, in the form of very pure metal, may be introduced in thechamber (step 504). To introduce the molten metal, a flow tube may beused to flow in the metal from a metal containing reservoir to thechamber. If necessary, pressure may be used to force the metal throughthe fill tube, for example, through overpressure of the metal-containingreservoir or a pump. The temperature of the reservoir and the fill tubemay be maintained above the melting point of the metal to facilitatemetal flow.

Dopants may be introduced in the chamber (step 506). The dopant may beintroduced as a dopant precursor. The dopant precursor may be flowedinto the chamber from a dopant source.

The temperature within the chamber may be raised to between about 800degrees Celsius to about 1300 degrees Celsius, and the pressure may beraised to at least one dimension greater than about 1 meter, for aperiod greater than about 30 minutes (step 508). In step 510, anitrogen-containing gas may be introduced in the chamber. The gas may beflowed from a nitrogen-containing gas source through an inlet into thechamber. The flow rate of the nitrogen-containing gas may be greaterthan about 250 (standard) cubic centimeters per minute.

A halide-containing gas may be introduced into the chamber (step 512).Optionally, steps 510 and 512 may be interchanged. The flow rate of thehalide-containing gas may be greater than about 25 cubic centimeters perminute. The ratio of the flow rate of the nitrogen-containing gas to theflow rate of the halide-containing gas may be about 10:1.

The metal may react with the nitrogen-containing gas in the presence ofthe halide to form a metal nitride (step 514). The halide affects thereaction between the metal and the nitrogen-containing gas in adetermined manner.

The reaction may proceed through a vapor transport and/or a wickingeffect. The metal nitride crust may form on top of the molten metalwithin the crucible. The crust may be slightly porous. The metal may bevapor transported or, if liquid, wicked to the top of the crust throughthe pores and react with the nitrogen-containing gas. The reaction maydeposit additional metal nitride and add to the crust. The reactionproceeds until virtually all the metal has undergone reaction.Additional metal may be flowed into the chamber from the reservoir.

The chamber may be cooled in step 516. The excess nitrogen-containinggas and hydrogen halide flows out from the reaction zone and ammoniumhalide may condense on cooler regions of the chamber. In one embodiment,the outlet may be kept hot so as to facilitate downstream trapping ofammonium halide; or alternatively a cold wall section may beincorporated to facilitate condensation of the ammonium halide. Thechamber may be opened on the outlet side to minimize leakage through theinlet side. The metal nitride may be removed through the outlet side.

Optionally, the metal nitride formed may be further processed (step518). In one embodiment, at least one surface of the metal nitride maybe subjected to one or more of scraping, scouring or scarifying. Thesurface may be further subjected to oxidation in air or in dry oxygenand it may further be boiled in perchloric acid. For use as a sputtertarget, the metal nitride may be trimmed, and the front and backsurfaces may be ground, lapped, and/or polished. The residualcontamination resulting from the post-processing step may be removed bywashing, sonicating, or both. Washing and sonicating may be performedin, for example, organic solvents, acids, bases, oxidizers (such ashydrogen peroxide), and the like. The metal nitride may be annealed inan inert, nitriding, or reducing atmosphere. The annealing may also beperformed in pure ammonia at a temperature of about 800 degree Celsiusto about 1200 degree Celsius for a period of time in a range of fromabout 30 minutes to about 200 hours.

Other processing may be done for use as a source material forcrystalline composition growth. For use as a source material, the metalnitride may be pulverized into particulate. The particles may have anaverage diameter in a range of from about 0.3 millimeters to about 10millimeters. The pulverizing may be carried out through, for example,compressive fracture, jaw crushing, wire sawing, ball milling, jetmilling, laser cutting, or cryo-fracturing. Post pulverization cleaningoperations may remove adventitious metal introduced by the pulverizationoperation, un-reacted metal, and undesirable metal oxide.

Rather than pulverizing, a thin platinum (Pt) film may be sputtered ontothe surface of metal nitride polycrystalline material. The sputteredsurface may be etched using a solution of methanol; hydrogen fluoride;and hydrogen peroxide. The catalytic reduction of peroxide on the Ptsurface may inject electron-hole pairs on the metal nitride. Theseelectron/hole pairs may be subject to in-plane drift and may assist thechemical etching. The result may be pores formed in the metal nitride,and the pores placement and dimensions may be controlled by thesputtering and etching process.

The examples provided are merely representative of the work thatcontributes to the teaching of the present application. Accordingly,these examples are not intended to limit the invention, as defined inthe appended claims.

EXAMPLES Example 1 Preparation of Polycrystalline Gallium Nitride

About 100 grams of gallium metal is placed in each of three polyethylenebottles. The polyethylene bottles are immersed in water that is hotenough to melt the gallium metal. Gallium has a melting point of about29.8 degree Celsius.

The molten metal is transferred to a cylindrical quartz crucible. Thecrucible has a graphite liner of about 12.5 micrometers thickness. Thecrucible has an outer diameter of about 4 centimeters and a length ofabout 20 centimeters. About 297.2 grams net of gallium is transferred tothe crucible. The liquid metal forms a layer with a maximum thickness ofabout 1 centimeter in the crucible. Argon gas is passed over the liquidgallium metal to cool and to blanket the metal. The liquid galliumsolidifies in the crucible as it cools.

The crucible is placed inside a horizontal quartz reactor tube with a250 micrometers thick graphite foil liner. The horizontal quartz tubenests inside a horizontal quartz reactor tube. The inner quartz tubewith the graphite foil liner serves to protect the quartz reactor, whichis susceptible to cracking during cooling. The cracking may beattributable to gallium nitride deposits on the inner wall during a run,and the thermal expansion mismatch between the quartz and the galliumnitride.

The reactor is evacuated and flushed several times with high purityargon gas. The flow rate of the argon gas is maintained at 50 cubiccentimeters per minute. High purity anhydrous ammonia is introducedthrough tubing inlets into the reactor at a rate of 100 cubiccentimeters per minute. The temperature inside the reactor is increasedusing a Lindberg split furnace. The flow of argon/ammonia gas mixturecontinues for about two hours. During that time, the temperature isramped steadily until the soak temperature of about 980 degree Celsiusis reached. Once the soak temperature is reached, the argon flow isstopped and, the flow rate of ammonia is increased to 200 cubiccentimeters per minute. High purity hydrogen chloride (HCl) gas isintroduced into the reactor at a flow rate of 25 cubic centimeters perminute.

The ammonia and HCl gases are purified using in-situ purifiers directlybefore being added. Aeronex Model SS-500KF-Y-4R is used for purifyingammonia, and Aeronex Model 45-03493 is used for purifying HCl. Aeronexis commercially available from Mykrolis Corporation (San Diego, Calif.).The purification reduces the levels of moisture, oxygen and otherimpurities. After temperature soaking the reactor for 24 hours at 980degree Celsius, the HCl gas flow is turned off. The reactor is kept atthe soak temperature of 980 degree Celsius for 20 minutes. The furnaceis cooled to 300 degree Celsius with a gradual temperature ramp downover a period of about 2 hours. Argon gas is then reintroduced at a flowrate of 50 cubic centimeters per minute, and the ammonia gas flow isturned off. The reactor is cooled to room temperature under an argonblanket.

The gallium in the crucible converts to a crust of polycrystallinegallium nitride filling the upper portion of the crucible. No metallicgallium is visible. The net weight changes to 345.7 grams, whichrepresents a weight increase of 16.3 percent. The theoretical weightincrease is 20.1 percent if the gallium is fully converted to thestoichiometric gallium nitride, and there is no loss due to recovery orvaporization as gallium halide.

Part of the polycrystalline gallium nitride crust is prepared forchemical analysis and other characterization. Analysis of thepolycrystalline gallium nitride is carried out by interstitial gasanalysis (IGA and shows an oxygen content of 16 parts per million (w/w).The gallium nitride shows a hydrogen content of less than 3 parts permillion, which is within the detection limit of the instrument. Thepolycrystalline gallium nitride is also analyzed by glow discharge massspectrometry (GDMS), and Table 1 summarizes the results for threesamples.

The SEM image given in FIG. 7 show the cross-section of thepolycrystalline GaN. The growth surface of the polycrystalline GaN at300 times magnification is shown in FIG. 8. The polycrystalline GaN isfound to have a columnar structure with the c-axis closely aligned withthe growth direction.

Two rectangular prisms are cut from the polycrystalline gallium nitrideand the faces and edges ground flat. The apparent densities aredetermined by measuring the weights and dimensions of the prisms. Thetwo pieces have apparent densities of 5.72 and 5.69 grams per cubiccentimeter, corresponding to 93.8 and 93.3 percent of the theoreticalvalue, respectively.

Example 2 Preparation of Polycrystalline Gallium Nitride

Example 2 is similar to Example 1, except that a larger load is used ina longer crucible. About 500 grams of gallium are used in this examplerather than 300 grams of gallium in Example 1. Also, the soakingtemperature is increased from 980 degree Celsius in the Example 1 to1000 degree Celsius in Example 2.

Gallium metal is placed in 5 polyethylene bottles, each bottlecontaining 100 grams of gallium. The gallium metal is melted andtransferred to a quartz crucible for a net of 497.3 grams of gallium.Following the steps described in Example 1, the crucible with solidifiedgallium is placed in the reactor.

The gallium in the crucible converts to a crust of polycrystallinegallium nitride. The crust does not have any visible metallic gallium.The net weight is 565.9 grams, which represents a weight increase of13.8 percent. Some of the polycrystalline gallium nitride crust ispulverized for chemical analysis and other characterization. Thepolycrystalline gallium nitride is analyzed for oxygen and hydrogen byIGA and shows an oxygen content of 64 parts per million oxygen and ahydrogen content of less than. 3 parts per million. GDMS analysis forthe presence of other elements produced results that are included inTable 1.

Example 3 Preparation of Polycrystalline Gallium Nitride

This example is similar to Examples 1 and 2, except a smaller load isused. About 200 grams of gallium versus the 300 grams of gallium ofExample 1. Other changes include a shorter temperature soak time (20hours versus 24 hours), and higher ammonia and hydrogen chloride flowrates. The flow rates are 600 cubic centimeters per minute of ammoniaand 30 cubic centimeters per minute of hydrogen chloride versus the 200cubic centimeters per minute of ammonia and the 25 cubic centimeters perminute of hydrogen chloride.

The gallium in the crucible converts to a crust of polycrystallinegallium nitride. There is no visible metallic gallium. The net weight is231.3 grams, which represents a weight increase of 16.7 percent. Some ofthe polycrystalline gallium nitride crust is broken for chemicalanalysis and other characterization. Analysis of the polycrystallinegallium nitride by IGA shows 71 parts per million oxygen and less than 3parts per million hydrogen. GDMS analyses of other elements are includedin Table 1.

TABLE 1 IGA/GDMS Analysis of Polycrystalline GaN Concentration (weightppm) Element Example 1 Example 2 Example 3 H <3 <3 <3 Li <0.005 <0.005<0.005 B 0.02 0.12 0.008 C <5 <2 3.3 O 16 64 71 F <0.01 <0.01 <0.01 Na<0.005 0.02 0.008 Mg 0.17 0.04 0.17 Al 0.21 0.21 0.07 Si 0.83 0.27 0.31P 0.02 0.04 0.83 S 0.62 0.62 <0.05 Cl 2.4 1.3 0.12 K <0.05 <0.05 <0.05Ca 0.75 <0.05 <0.05 Ti <0.005 <0.005 <0.005 Cr 0.02 <0.005 0.02 Mn <0.01<0.01 <0.01 Fe 3.3 0.21 0.37 Co <0.005 <0.005 <0.005 Ni 0.008 <0.005<0.005 Cu <0.005 <0.005 <0.005 Zn <0.05 <0.05 <0.05 Mo <0.05 <0.05 <0.05Ag <0.5 <0.5 <0.5 W <0.01 <0.01 <0.01 Au <0.1 <0.1 <0.1

Example 4 Preparation of Polycrystalline Gallium Nitride

While Examples 1-3 illustrate polycrystalline gallium nitride synthesisperformed in a small laboratory reactor with a single crucible, Example4 illustrates a run made with a scaled-up reactor. The reactor has anouter diameter of 15 centimeters, and into which four smaller quartzinner tubes each having a 59 millimeter outer diameter is placed. Agraphite foil liner such as the one in Example 1 is placed in thereactor. Two crucibles each are placed in the four inner quartz tubesalong a 3-Zone THERMCRAFT split furnace.

Example 4 follows the procedure of Example 3 unless stated otherwise.The reactor is evacuated and purged with 99.999% purity argon gasseveral times. The argon gas flow rate is maintained at 1400 cubiccentimeters per minute and 99.99995% purity ammonia is introduced at1200 cubic centimeters per minute. The reactor is heated in theargon/ammonia mixed flow to a soak temperature of 1000 degree Celsius inabout 4 hours. When the soak temperature is reached, the argon flow rateis reduced to 200 cubic centimeters per minute, the ammonia flow rate isincreased to 2400 cubic centimeters per minute, and 99.999% purityhydrogen chloride (HCl) gas is introduced at a flow rate of 200 cubiccentimeters per minute. The ammonia and HCl gases are used with in-situpurifiers (Aeronex Model CES500KFSK4R for ammonia, and Aeronex ModelCE500KFC4R for HCl). After a soak period of 24 hours at 1000 degreeCelsius, the HCl flow is turned off, and the furnace is cooled to about650 degree Celsius over 5 hours. An argon flow is introduced through theammonia line at a flow rate of 600 cubic centimeters per minute, theammonia flow is then turned off, and the reactor is cooled to roomtemperature in an argon blanket.

The gallium in each of the four crucibles converts to crusts ofpolycrystalline gallium nitride. No metallic gallium is visible. Some ofthe polycrystalline GaN is taken for chemical analysis and othercharacterizations. Oxygen analysis is carried out on duplicate samplesusing IGA and duplicate samples using LECO. The four results show 71parts per million and 63 parts per million oxygen by IGA, and 30 partsper million and 63 parts per million oxygen by LECO.

Strength test specimens are prepared from the polycrystalline galliumnitride. The polycrystalline GaN crusts are cut, ground, lapped andpolished into discs of about 1.25 centimeters in diameter and 0.75centimeters thick. The specimens are weighed to obtain the apparentdensity. The results are summarized in Table 2. The apparent densitieslie in the range of 5.36 to 5.51 grams per cubic centimeter,corresponding to 87.8 to 90.4 percent of the theoretical density and anapparent porosity between 9.6 and 12.2 percent.

TABLE 2 Polycrystalline GaN apparent density results: Apparent %Theoretical Sample density (g cm⁻³) density 001-2 5.51 90.4 001-3 5.3788.0 002-2 5.36 87.8 002-4 5.50 90.2

The specimens are then tested using the ring-on-ring MonotonicEquibiaxial Test Method described in ASTM C1499. The testing machineused is an INSTRON Series IX screw type with a loading rate of 30 to 35MegaPascal per second. The diameter of the supporting ring and loadingring are 11.91 millimeters and 6 millimeters, respectively. Both ringshave a contact radius of 0.25 millimeter. To reduce friction, 0.127 mmthick graphite foil discs are placed between the specimens and therings. Maximum load for each specimen is taken from loading data, whichis recorded every 0.05 milliseconds during the test. Maximum strengthfor each specimen is calculated in accordance with the standard. Thetest results on a total of 8 specimens (four each from twopolycrystalline gallium nitride synthesis runs) are as given in Table 3,below. A graph of the bend strength of gallium nitride is given in FIG.9.

TABLE 3 Polycrystalline GaN strength test results: Strength (MPa) Mean67.96 Standard Dev 10.73 Minimum 51.78 Maximum 85.75

The embodiments described herein are examples of compositions,structures, systems and methods having elements corresponding to theelements of the invention recited in the claims. This writtendescription may enable one of ordinary skill in the art to make and useembodiments having alternative elements that likewise correspond to theelements of the invention recited in the claims. The scope thus includescompositions, structures, systems and methods that do not differ fromthe literal language of the claims, and further includes othercompositions, structures, systems and methods with insubstantialdifferences from the literal language of the claims. While only certainfeatures and embodiments have been illustrated and described herein,many modifications and changes may occur to one of ordinary skill in therelevant art. The appended claims are intended to cover all suchmodifications and changes.

1. A composition, comprising: a polycrystalline group III metal nitridehaving a plurality of grains, and the grains having a columnarstructure, wherein an average grain diameter is larger than about 10micrometers; and, one or more of the metal nitride having an impuritycontent of less than about 200 parts per million; the metal nitridehaving a porosity in volume fraction in a range of from about 0.1percent to about 30 percent; or the metal nitride having an apparentdensity in a range of from about 70 percent to about 99.8 percent of thetheoretical density value corresponding to the metal nitride.
 2. Thecomposition as defined in claim 1, wherein the metal comprises one ormore of aluminum, indium, or gallium.
 3. The composition as defined inclaim 1, wherein the average number of grains in the plurality is in arange of from about 100 per cubic centimeter to about 10,0000 per cubiccentimeter.
 4. The composition as defined in claim 1, wherein theporosity of the metal nitride in volume fraction is in a range of fromabout 0.1 percent to about 10 percent.
 5. The composition as defined inclaim 1, wherein the porosity of the metal nitride in volume fraction isin a range of from about 10 percent to about 30 percent.
 6. Thecomposition as defined in claim 1, wherein an average grain diameter isgreater than about 1 millimeter.
 7. The composition as defined in claim1, wherein an atomic fraction of the metal in the metal nitride is in arange of from about 0.49 to about 0.55.
 8. The composition as defined inclaim 1, wherein the impurity content of the metal nitride is in a rangeof from about 100 parts per million to about 5 parts per million.
 9. Thecomposition as defined in claim 1, wherein the impurity consistsessentially of oxygen.
 10. The composition as defined in claim 9,wherein the oxygen content of the metal nitride is less than about 100parts per million.
 11. The composition as defined in claim 9, whereinthe oxygen content of the metal nitride is in a range of from about 100parts per million to about 20 parts per million.
 12. The composition asdefined in claim 9, wherein the oxygen content of the metal nitride isless than about 20 parts per million.
 13. The composition as defined inclaim 1, wherein the apparent density of the polycrystalline metalnitride is in a range of from about 85 percent to about 95 percent ofthe theoretical value.
 14. The composition as defined in claim 1,wherein the atomic fraction of the metal in the metal nitride is in arange of from about 0.50 to about 0.51.
 15. The composition as definedin claim 1, further comprising one or more dopants.
 16. The compositionas defined in claim 15, wherein the dopants are capable of producing oneor more of n-type material, p-type material, or semi-conductingmaterial.
 17. The composition as defined in claim 15, wherein thedopants are capable of producing one or more of a semi-insulatingmaterial, a magnetic material, or a luminescent material.
 18. Thecomposition as defined in claim 15, wherein the dopant concentration isgreater than about 10²¹ atoms per cubic centimeters.
 19. The compositionas defined in claim 15, wherein the dopant concentration is in a rangeof from about 10²¹ atoms per cubic centimeters to about 10¹⁶ atoms percubic centimeters.
 20. The composition as defined in claim 1, whereinthe polycrystalline metal nitride has an inter-grain bend strengthgreater than about 20 MegaPascal.
 21. The composition as defined inclaim 1, wherein the polycrystalline metal nitride has an inter-grainbend strength that is in a range of from about 20 MegaPascal to about 90MegaPascal.
 22. The composition as defined in claim 1, wherein thepolycrystalline metal nitride has an inter-grain bend strength greaterthan about 90 MegaPascal.
 23. A composition, comprising: apolycrystalline group III metal nitride having a plurality of grains,and the grains having a columnar structure; the grains having an averagegrain diameter larger than about 10 micrometers; and wherein thepolycrystalline metal nitride has an inter-grain bend strength greaterthan about 20 MegaPascal.
 24. The composition as defined in claim 23,the metal nitride having a halide content in an amount of less thanabout 2.4 parts per million.
 25. The composition as defined in claim 24,wherein the halide comprises chlorine.
 26. A composition, comprising: apolycrystalline group III metal nitride having a plurality of grains,the grains having an average grain diameter larger than about 10micrometers, and the grains having a columnar structure wherein a ratioof an average grain size to an average grain diameter is in a range ofgreater than about
 2. 27. The composition as defined in claim 26,wherein the metal nitride comprises gallium nitride.
 28. The compositionas defined in claim 26, wherein the metal nitride comprises aluminumnitride.